They have dedicated registers to hold these values for interrupts, exceptions and supervisor calls.
2.
Some third-party x86 equivalent processor even became noncompetitive to ARM due having no dedicated register file architecture.
3.
It contains 57 instruction set, eight entries 64 bit vector registers ( same MM0 ~ MM7 register naming that mapped on x87 stack, only different is i750 has dedicate register while the x86 mmx cpu did not included.
4.
Perhaps the reason Boolos-Burgess-Jeffrey clear r3 is to facilitate an unconditional jump to " loop "; this is often done by use of a dedicated register " 0 " that contains " 0 ":
5.
Processors in embedded systems, which have higher requirements for real-time behaviors, might support multithreading by decreasing the thread-switch time, perhaps by allocating a dedicated register file for each thread instead of saving / restoring a common register file.